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Reverse DNS

Reverse DNS (rDNS) is a critical DNS record that maps your IP address back to a hostname. It’s an essential part of sender authentication and helps mailbox providers verify the legitimacy of your sending IP.

What is reverse DNS?

When mailbox providers receive your email, they often perform a reverse DNS lookup on your sending IP to confirm it maps back to a trusted domain.

  • A valid rDNS record increases your chances of inbox placement
  • Missing or mismatched rDNS records can trigger spam filters

Available only for dedicated IPs

MX18 supports rDNS configuration only for dedicated IPs.

If you're using shared IPs, MX18 handles rDNS using our default branded infrastructure domain — no action is needed on your end.

📌 If you are on a dedicated IP and haven’t configured reverse DNS, we highly recommend setting it up to establish domain ownership and boost credibility.

Example DNS record

To configure reverse DNS for your dedicated IP, your provider (or MX18, if hosting the IP) will set the PTR record like this:

163.223.88.2 → smtp.yourdomain.com

This should match the domain you use in your from address and HELO/EHLO SMTP handshake.

Verify and you're done

Once the PTR record is set by your hosting provider or through MX18:

  • You can verify rDNS resolution using tools like dig or mxtoolbox.com
  • Mailbox providers will now recognize your IP as belonging to your domain

No further steps are needed. rDNS setup is complete!

Need help?

  • Unsure if you’re eligible for rDNS?
  • Need help updating your DNS or PTR records?

Contact support@mx18.com and we’ll walk you through it.